Method for forming fibrous pads

ABSTRACT

Method for the dry forming of fibrous pads employ a pad forming member closing the lower end of a pad forming area. The pad forming member preferably is in the form of a condenser roll having three-dimensional pockets, or cavities about the periphery thereof. Each cavity includes an opening into it, and the cavities are brought into communication with the pad forming area as the condenser roll is continuously driven during operation of the apparatus. Each cavity is defined by foraminous bottom and side surfaces, the surface area of which is greater than the surface area of the opening into it. An air suspension of fibers is formed in the pad forming area, and a vacuum is applied through the foraminous surfaces of each cavity when it is disposed in the pad forming area to pull the air of the suspension through the foraminous surfaces, and deposit the fibers carried in the air suspension onto the foraminous surfaces in the form of a fibrous layer. A transfer conveyer is fed in overlying relationship with the opening of each cavity downstream of the pad forming area, and a vacuum is applied through the transfer conveyer to transfer the fibrous layer from each cavity onto the transfer conveyer. The fibers deposited on the transfer conveyer are confined to an area substantially equal to the surface area of the opening into each cavity, and accordingly, the fibers are consolidated as they are transferred from each cavity onto the transfer conveyer to form fibrous pads having a greater basis weight than the basis weight of the fibrous layers formed within the cavities.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus and method for dry formingfibrous pads, and specifically, to apparatus and method for formingfibrous pads suitable for use by themselves, or in conjunction withother components to form sanitary products such as disposable diapers,sanitary napkins and the like.

2. Description of the Prior Art

Apparatus and method for forming absorbent fibrous pads are known in theprior art. Such fibrous pads are often formed from 100% woodpulp fibers,and are utilized as internal absorbent components in sanitary productssuch as disposable diapers, sanitary napkins and the like. In many ofthese applications the fibrous pads are required to have a relativelyhigh basis weight. For example, the center region of the absorbent padshown in FIG. 3 of U.S. Pat. No. 3,766,922 issued on Oct. 23, 1973, andassigned to Scott Paper Company, has a basis weight of approximately 45oz/yd.².

It has been suggested to dry form fibrous pads directly intothree-dimensional pockets, or cavities of pad forming members whichclose the lower end of a pad forming area in conventional dry formingequipment. The pad forming member can be in the form of a cylindricalcondenser roll having a three-dimensional pocket formed therein, oralternatively, can be in the form of a foraminous belt havingthree-dimensional pockets formed therein. In these prior art apparatusthe fibrous pads are directly formed into the pockets by applying avacuum through only the lower, or bottom surface of the pockets, i.e.,only the bottom surface is foraminous. When the pad forming member is inthe form of a cylindrical condenser roll the side walls of eachthree-dimensional pocket converge toward each other in a direction fromthe outer periphery of the condenser roll to the bottom surface, andaccordingly, the surface area of the bottom surface of each pocket isless than the surface area of the opening into it.

In other prior art apparatus and methods fibrous pads are directlyformed on a cavity-free outer foraminous surface of a cylindricalcondenser roll or foraminous belt.

Accordingly, in the prior art apparatus and methods the foraminoussurface through which the vacuum is applied either has substantially thesame area (the outer surface of a condenser roll or belt), or a lesserarea (the bottom surface of a pocket in a condenser roll) than the areaof the fibrous pad which ultimately is to be formed.

When fibers are initially deposited as a layer on a foraminous surfacefrom an air suspension they establish increased resistance to air flowthrough said surface. This resistance to air flow increasessignificantly with slight increases in basis weight of the fibrous layerformed on the foraminous surface. This resistance to air flow can becomeso great as to prevent the required volume of air containing suspendedfibers to be pulled through the foraminous surface to form a fibrous padhaving a desired basis weight. Even the use of uneconomical, highhorsepower vacuum pumps to establish high vacuum levels may not solvethe problem, since the high vacuum levels may merely consolidate thefibers into an air-impervious layer on the foraminous surface before therequisite weight of fibers is deposited in said cavity. When the vacuumlevel is adjusted to avoid excessive compaction of the fibrous layer thelarge resistance to air flow through the layer still makes it necessaryto employ a long formation area to form fibrous pads of a high basisweight. Accordingly, excessively large equipment taking up valuableplant space may be required. The instant invention overcomes theproblems set forth in this paragraph.

SUMMARY OF THE INVENTION

The method and apparatus of this invention resides in initially forminga fibrous layer on foraminous surfaces of a three-dimensional pocket orcavity having a greater surface area than the area of a fibrous padwhich is to be formed therefrom. The critical feature of the method andapparatus of this invention is that the surface area of the foraminoussurfaces of each cavity is greater than the area of the opening into it.Accordingly, a predetermined total weight of fibers can be deposited onthe foraminous portions of the cavity in the form of a fibrous layerincompletely filling the cavity, and having a lower basis weight(weight/unit area) than can be deposited on a surface having the same orlesser area than the cavity opening. Since the pressure drop which hasto be established through a foraminous surface to direct a gastherethrough increases with increased basis weight of a fibrous layerthereon, a lesser pressure drop has to be established through theforaminous surfaces defining each cavity to deposit a predeterminedtotal weight of fibers therein, than would have to be established if thesame total weight of fibers were deposited on a foraminous surface ofsubstantially the same, or lesser area than the area of the cavityopening.

After the fibrous layer is formed within each cavity, means are providedto transfer allegiance of the layer to a transfer conveyer which isdirected in overlying contacting relationship with the forming member soas to overlie the opening into each cavity. In the preferred embodimentof the invention the transfer conveyer is foraminous and a vacuum isapplied therethrough to transfer allegiance of the fibrous layer fromeach cavity to the transfer conveyer to thereby form the fibrous pads onsaid transfer conveyer. The fibrous pads have a greater basis weightthan the fibrous layers from which they are formed. This results fromthe consolidation of the fibrous layers into a smaller area on thetransfer conveyer than they occupied within the cavities. To furtherexplain, the fibrous layer from each cavity is transferred to thetransfer conveyer over an area substantially equal to the area of theopening into the cavity. The area of the cavity opening is less than theforaminous surface area of the cavity defined by the base and sidesurfaces thereof. Accordingly, the fibrous layer is confined to a lesserarea on the transfer conveyer than it occupied in the cavity; therebyresulting in the formation of a pad which has a greater basis weightthan the fibrous layer formed in the cavity. Therefore, this inventionpermits the formation of a fibrous layer having a lower basis weightthan a fibrous pad which ultimately is to be formed, and accordinglypermits the use of low cost, low horsepower vacuum sources to form sucha fibrous pad and/or the use of reasonably sized equipment which doesnot take up excessive plant space.

Further objects and advantages of this invention will become apparentupon reading the detailed description which follows taken in conjunctionwith the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic isometric view of an apparatus according to thisinvention;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3;

FIG. 5 is a sectional view taken along line 5--5 of FIG. 3;

FIG. 6 is an isometric view showing a part of a pad forming memberaccording to an alternative embodiment of this invention;

FIG. 7 is a sectional view taken along line 7--7 of FIG. 6;

FIG. 8 is a plan view of a fibrous pad formed by employing the padforming member shown in FIG. 6; and

FIG. 9 is a sectional view taken along line 9--9 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, the apparatus 10 for manufacturing dry formedfibrous pads 60 includes feed rolls 12 for directing a fibrous feed mat14 into engagement with a fiberizing roll 16. The fiberizing roll 16includes surface clothing including pins or teeth 18 projectingtherefrom. A shroud 20 encloses the fiberizing roll 16 to define a padforming area 22. The pad forming area is closed at its lower end by apad forming member in the form of a cylindrical condenser roll 24 whichis driven by suitable drive means (not shown) in the direction indicatedby arrow 26 (FIGS. 1 and 3). The above-described structural features, orequivalents thereof, are conventional in many prior art apparatus forforming dry formed fibrous webs or pads. For example, the Rando-Webbermanufactured by Curlator Corporation of Rochester, N.Y., employessimilar structural elements which can be utilized in this invention.

Referring to FIGS. 1 - 3, unique structural features of the condenserroll 24 of this invention will be described. The condenser roll 24includes a plurality of three-dimensional pockets, or cavities 28uniformly spaced about the periphery thereof. The number of cavities 28can be varied depending upon the size of the roll, and the number ofpads which one desires to form. In the embodiment shown in thisinvention the roll contains six cavities.

Each cavity 28 includes a foraminous, concave base 30 providing thebottom region and part of the side region of the cavity (FIG. 2). Thecavities 28 additionally include foraminous side surfaces 32 joined tothe concave base 30 and diverging outwardly therefrom to complete thecavity construction (FIGS. 1 and 3). The upper margins of each cavityterminate substantially in alignment with the outer periphery of thecondenser roll, and define an opening 34. In the embodiment shown inFIGS. 1 - 3 the outer periphery of the condenser roll 24 isair-impervious.

A critical feature of this invention is that the foraminous surface areaof each cavity 28 provided by the foraminous concave base 30 and theside surfaces 32 is greater than the area of the cavity opening 34 boundby the upper margins of each of said cavities 28. The importance of thisfeature will be explained later in the application.

Referring to FIG. 3, a cylindrical vacuum chamber 38 is mounted withinthe interior of the condenser roll 24, and is secured to fixed framework(not shown) to prevent rotation thereof. The cylindrical vacuum chamber38 is connected to a suitable source of vacuum, such as the low pressureside of a fan (not shown). A lower hemispherical portion 40 of thevacuum chamber 38 is either constructed of an air-impervious member, orcoated with a suitable material to render it air-impervious. The upperhemispherical portion 42 is air-pervious. A plurality of partitions 44are fixedly connected to the outer shell of the condenser roll 24, andeach partition has a sealing bushing 46 which is maintained infrictional, sliding engagement with the outer surface of the vacuumchamber 38. The partitions are connected to the condenser roll 24intermediate adjacent cavities 28.

Referring to FIGS. 1 and 3, a foraminous transfer conveyer 48 is trainedabout a plurality of mounting rolls 50, 52 and 54, respectively. Anynumber of rolls can be utilized; however, the rolls should be arrangedso that the transfer conveyer 48 is mounted in partial wrappingengagement with the condenser roll 24 downstream of the pad forming area22. One or more of the transfer conveyer mounting rolls is positivelydriven to drive the transfer conveyer 48 in the direction indicated byarrows 56. A transfer vacuum box 58 is positioned beneath the upper runof the transfer conveyer 48 underlying the region of the upper run whichis in wrapping engagement with the condenser roll 24. A partial vacuumis established through the vacuum box 58 by any conventional source ofvacuum, such as a fan (not shown).

Referring to FIGS. 1 and 3, the operation of the apparatus 10 of thisinvention will be described. The feed mat 14 is directed into engagementwith the fiberizing roll 16 by the feed rolls 12. The fiberizing roll isrotatably driven at a high speed to separate fibers from the feed mat 14and direct them into the pad forming area 22 to form an air suspensionof substantially individualized fibers within said pad forming area. Apartial vacuum is established through the cylindrical vacuum chamber 38as the condenser roll 24 is moved in the direction indicated by arrow26. As a cavity 28 enters the forming area (Zone I - FIG. 3) it is inalignment with the foraminous region 42 of the vacuum chamber 38.Accordingly, the vacuum applied through the vacuum chamber 38establishes a pressure drop across the foraminous base 30 and sidesurfaces 32 of the cavity 28. This pressure drop is effective to pullthe air of the suspension through the cavity, and to deposit fibers inthe suspension in the pocket in the form of a fibrous layer 59. As thecavity continuously travels through the pad forming area 22 the fiberscontinuously build up in the layer 59 until complete formation of thelayer 59 is establishes at Zone II.

Referring to FIGS. 3 and 4, the foraminous layer 59 is deposited oversubstantially the entire foraminous region of the cavity 28 andincompletely fills said cavity. As explained earlier in thisapplication, the surface area of the foraminous portion of each cavity28 is greater than the area of the cavity opening 34. Accordingly, apredetermined total weight of fibers can be deposited on the foraminousportions of the cavity with a lower basis weight (weight/unit area) thancan be deposited on a foraminous surface of a lesser area, such as bydepositing the fibers on a region of the outer surface of the condenserroll 24 corresponding in area to that of the cavity opening 34. Sincethe pressure drop which has to be established through a foraminoussurface to direct air therethrough increases with increased basis weightof a fibrous web or layer thereon, a lesser pressure drop has to beestablished through the foraminous surfaces defining cavities 28 todeposit a predetermined total weight of fibers therein, than would haveto be established if the same total weight of fibers were deposited on aforaminous surface of a lesser area.

As a cavity 28 leaves Zone II (FIG. 3) of the forming area, the upperrun of transfer conveyer 48 is moved into engagement with the outerperiphery of the condenser roll 24 in overlying relationship with thecavity opening 34. Also, the cavity 28 is in alignment with maskedportion 40 of the cylindrical vacuum chamber 38 so that the partialvacuum which is established through the vacuum chamber 38 is ineffectiveto retain the fibrous layer 59 within the pocket. In this same locationthe pocket opening 34 is in overlying relationship with the transfervacuum box 58, through which a partial vacuum is established. Thispartial vacuum is effective to transfer allegiance of the fibrous layer59 from the pocket 28 to the transfer conveyer 48 to thereby form afibrous pad 60 (FIGS. 3 and 5).

The fibrous pad 60 has a greater basis weight than the fibrous layer 59from which it is formed. This results from the consolidation of thefibrous layer 59 into a smaller area on the transfer conveyer 48 than itoccupied within the cavity 28. To further explain, the fibrous layer 59from the pocket 28 is transferred to the transfer conveyer 48 over anarea substantially equal to the area of the pocket opening 34. The areaof the cavity opening 34 is less than the foraminous area of the cavity28 defined by the base 30 and side surfaces 32. Accordingly, the fibrouslayer 59 is confined to a lesser area on the transfer conveyer 48 thanit occupied in the cavity 28; thereby resulting in the formation of apad which has a greater basis weight than the fibrous layer 59 formed inthe cavity 28.

Since the partial vacuum established through each cavity 28 isestablished through the entire area upon which the fibrous layer 59 isformed, the method and apparatus of this invention permits the formationof high basis weight fibrous pad 60 with the use of less costly, lowerhorsepower vacuum sources than can be utilized in the prior artapparatus and methods. To further explain, the present invention permitsthe formation of a fibrous pad 60 of a given basis weight by utilizing avacuum source which need only be capable of establishing a partialvacuum of a sufficient level to form a fibrous layer 59 having a lowerbasis weight. The lower basis weight of the fibrous layer 59 within eachcavity 28 establishes a lower resistance to air flow through theforaminous surfaces and fibrous layer 59 within each cavity 28 thanwould be established if the fibrous layer 59 were formed on a foraminoussurface having less surface area than the area of the foraminoussurfaces of the cavity 28. This lower resistance to air flow permits theuse of lower horsepower vacuum sources to achieve the final formation ofthe fibrous layer 59 in the method and apparatus of this invention.

The formed fibrous pads 60 (FIGS. 3 and 5) are maintained in engagementwith the transfer conveyer 48 as the condenser roll 24 separates fromthe pads by maintaining the application of a partial vacuum through thetransfer vacuum box 58 at the time of separation.

The formed pad 60 is conveyed by the transfer conveyer 48 to subsequentprocessing equipment (not shown) downstream of the apparatus 10. Forexample, such subsequent equipment can include converting equipment forencasing the fibrous pad 60 between a fluid pervious facing layer and afluid impervious (e.g. plastic) backing layer to form a disposablediaper or sanitary napkin.

Referring to FIGS. 6 and 7, an alternative construction of a condenserroll 24A is shown for forming fibrous pads 60A (FIGS. 8 and 9) havinghigh basis weight regions 62 and low basis weight regions 64 therein.Each fibrous pad 60A is formed on a region 66 of the condenser roll 24Awhich comprises a plurality of closely spaced cavities 28A separated byforaminous corridor regions 68. In all other respects the apparatus issubstantially identical to that disclosed in FIG. 1. The low basisweight regions 64 of the fibrous pad 60A correspond to the regions ofthe fibrous layer formed on the foraminous corridors 68, and the highbasis weight regions 62 correspond to the regions of the fibrous layerformed within the cavities 28A. The fibers deposited on the corridors 68(i.e., substantially planar regions) will build up to substantially thesame level or height as the fibers deposited within thethree-dimensional cavities 28A. However, due to the fact that theforaminous surface area of each cavity 28A is greater than the area ofthe opening into it, transfer of the fibrous layers from the cavities28A onto the transfer conveyer 48 will result in the formation of higherbasis weight pad areas 62 than that of the fibrous layer within eachcavity 28A. However, the fibrous layers deposited on the corridorregions 68 will be transferred to the transfer conveyer oversubstantially the same area as the corridor area, and accordingly,substantially no increase in basis weight will take place in theseregions. In this manner a pad having varying basis weights can beformed.

A pad having different basis weight regions can also be formed bygrouping cavities together having foraminous surfaces of differencysurface areas. When the fibrous layers formed in such a grouping ofcavities is transferred to a transfer conveyer, the basis weight indifferent sections of the pad will vary in relationship to the surfaceareas of the cavities from which the sections of the pad were formed.

Although certain preferred embodiments of this invention have beendisclosed; other modifications can exist. For example, the outerperiphery of the forming member 24 (FIG. 1) which surrounds each cavity28 can be completely foraminous. In such an embodiment, the fibrous pads60 which are formed from the fibrous layers 59 within each cavity 28will be integrally joined with fibrous web sections of a lower basisweight which are initiailly formed as layers on the foraminous outerperipheral regions of the condenser roll surrounding the cavities. Thissame modification can exist with respect to the forming member 24Adisclosed in FIGS. 6 and 7. Reference throughout this application,including the claims, to the formation of fibrous pads includes theformation of alternative web constructions as set forth in thisparagraph.

The fibrous feed mat 14 preferably is formed of woodpulp fibers havingan average fiber length less than one-fourth inch. However, it is withinthe scope of this invention to form fibrous feed mats from any type offibers, including blends of woodpulp fibers and longer textile-lengthfibers. For example, the fibrous feed mat 14 can include over 75% byweight woodpulp fibers with the remainder of the fibers being longertextile-length fibers, such as rayon, polyester, cotton, etc.

An illustrative example indicating the advantages which can be achievedaccording to the method of this invention will now be described. Thisexample is not intended to limit the broadest aspects of the invention,but is intended to illustrate the dramatic results which can be achievedby practicing the invention.

A cavity was formed in which the foraminous forming surface had anincrease in surface area of 70% as compared to the area of the openinginto the cavity defined by the upper margins thereof. Accordingly, ifone desired to form a fibrous pad 60 having a basis weight of 23.3oz./yd.², it would only be necessary to form a fibrous layer 59 in thepocket having a basis weight of 13.7 (i.e., 23.3/1.7). If the cavity ofthis invention were not employed, and the fibrous pad were to be formedon a surface having an area equal to the cavity opening defined by theupper margins thereof, the total basis weight of 23.3 oz./yd.² wouldhave to be formed on this surface. A pressure drop of approximately 80inches of water would have to be established to form a fibrous pad orlayer having a basis weight of 23.3 oz./yd.² when an air suspension offibres approaches the forming surface at 1550 feet per minute. However,at this same approach velocity (1550 feet per minute), a pressure dropof less than 48 inches of water would have to be established to form the13.7 oz./yd.² fibrous layer within the cavity. Accordingly, the pressuredrop requirement is greatly reduced to form a fibrous pad of a givenbasis weight by employing applicant's invention, as opposed to directlyforming the pad of the desired basis weight on an upper foraminoussurface having an area equal to that of the cavity opening defined bythe upper margins of the cavity. Since a lower pressure drop isrequired, lower horsepower, less costly vacuum equipment can beutilized, or alternatively, the same horsepower requirements can beutilized as in the prior art, and pad formation achieved over a smallerformation zone than in the prior art equipment to thereby permit the useof equipment which occupies less plant space.

What is claimed is:
 1. A method for forming a fibrous pad by employing aforming member including a cavity having a foraminous forming surfaceand upper margins defining an opening into said cavity, the area of theforaminous forming surface being greater than the area of the openingbound by the upper margins of said cavity, said method comprising thesteps of:A. forming a gaseous suspension of fibers; B. establishing apressure drop across the foraminous forming surface of the cavity todirect the gas of the suspension through the forming surface, and tocondense the fibers of the suspension onto the forming surface in theform of a fibrous layer incompletely filling said cavity; C. directing atransfer conveyor into overlying relationship with, and closely adjacentto the orfice of the cavity after the fibrous layer is formed in saidcavity; and D. transferring the fibrous layer to said transfer conveyorand confining said fibrous layer to a lesser area on the transferconveyor than it occupied on the foraminous forming surface to form afibrous pad having a greater basis weight than that of the fibrous layeron the foraminous forming surface.
 2. The method according to claim 1,wherein allegiance of the layer is transferred from the cavity to thetransfer conveyer by terminating the pressure drop across the foraminousforming surface of the cavity, and establishing a pressure drop acrossthe transfer conveyer while the pressure drop across the forming surfaceis terminated.